from3Points

Factory method to construct a circle which has the three given points
lying on its perimeter. The function returns null, if the 3 points are
co-linear (in which case it's impossible to find a circle).
Based on CPP code by Paul Bourke:
http://local.wasp.uwa.edu.au/~pbourke/geometry/circlefrom3/

getCircumference

Computes the approximate circumference of the ellipse, using this
equation: 2 * PI * sqrt(1/2 * (rx*rx+ry*ry)).
The precise value is an infinite series elliptical integral, but the
approximation comes sufficiently close. See Wikipedia for more details:
http://en.wikipedia.org/wiki/Ellipse